This invention generally relates to a wavelength division multiplexing transmitter and receiver module, and particularly relates to a wavelength division multiplexing transmitter and receiver module utilizing an etched silicon substrate as the mounting platform for the optical components and optoelectronic devices and a microstructure formed in the silicon substrate as the building base for the multiplexer and/or the demultiplexer.
In order to provide high bandwidth communications to the subscriber, some sophisticated system configurations based on full fiber-optic access network such as fiber-to-the-home (FTTH) or fiber-to-the-desktop (FTTD) are required. The technology for such systems exists, but it can not proliferate unless costs are reduced substantially, especially the costs of the opto-electronic network unit (ONU) working as a wavelength division multiplexing transmitter and receiver module. To make FTTH or FTTD economically feasible, several wavelength division multiplexing transmitter and receiver modules suitable for high-volume, low-cost manufacturing have been developed.
One such module, as shown in FIG. 1, comprises a sealed TO can transmitter 102 and a hermetically sealed TO can receiver 103 that are mounted in an orthogonal fashion in a common hollow housing 101 to effect the module. An optical fiber 108 is inserted in the housing through a connector 107. The optical fiber transmits light to and from the module via a spherical lens 106. An optical beamsplitter 105 supported by a spacer tube 104 can be wavelength dependent or a proportional splitter that deflects light in a defined intensity to the receiver or the detector. The wavelength selectivity requirement of the detector and the transmitter or the emitter is then effected by selective wavelength filtering prior to the light's impinging on the detector. The various subassemblies are then adjusted for optical alignment and finally fixed in final position.
The drawback to this configuration is that the autonomous emitter and detector are aligned in the common housing either iteratively or successively with the various optical elements of the system to optimize the input and output performance. This approach is clearly a complicated and labor intensive approach, which accordingly increases the cost of the devices. Furthermore, in the preferred embodiment, the lens element for the light emitter is within the encapsulation, and the optical alignment of this due to the close proximity of the lens to the emitter is rather difficult, and thus a labor intensive effort that serves to further increase the cost of manufacture.
Another wavelength division multiplexing transmitter and receiver module, as shown in FIG. 2, consists of three major parts: an optical block 201, an optical network unit chip 206, and an electronic block 210. On the optical block 201 side, an optical fiber 203 held in a V-groove of a silicon wafer 202 and coming from the subscriber line terminal is coupled to the planar microlens 205 where wavelengths of 1.3 .mu.m (digital voice signal) and 1.55 .mu.m (analog video signal) are converted into collimated optical beams. The optical network unit chip 206, fabricated by stacked planar optical technique, is composed of stacked glass slices coated by dielectric multilayered filters such as wavelength division multiplexing splitting filters 207, half-mirrors 209 and mirrors 208a, 208b. This unit is then sandwiched by planar microlens array blocks. At the optical network unit chip 206, wavelengths of 1.3 .mu.m and 1.55 .mu.m are split by the dielectric multilayered wavelength division multiplexing filter 207 in such way that 1.3 .mu.m wavelength is transmitted straight while the 1.55 .mu.m one is reflected. The wavelength of 1.3 .mu.m is reflected by the half-mirror 209 and the mirror 208b, focused by one of the microlenses of the planar microlens array, located next to the electronic block 210, and then detected by a 1.3 .mu.m photodetector 212. The wavelength of 1.55 .mu.m is reflected by the mirror 208a, focused by another microlens of the planar microlens array and detected by a 1.55 .mu.m photodetector 213 . For 1.3 .mu.m transmission, a light optical beam coming from the 1.3 .mu.m laser diode 211, located at the electronic block 210, is coupled with a microlens of the planar microlens array converting it into a collimated optical beam. Then, it enters the optical network unit chip 206, passing straight through the half-mirror 209 and the wavelength division multiplexing filter 207, and focused onto the optical fiber 203 located at the optical block 201 at the planar microlens array. Coupling between the planar microlens array 205 and the optical fiber 203 is realized by a put-in micro-connector scheme 204. The dielectric multilayered wavelength division multiplexing filters 207, half-mirrors 209 and mirrors 208a, 208b are fabricated by electron optical beam evaporation method on the glass substrate.
In this configuration the optical network unit and the planar microlens arrays block are not integrated in a single substrate. Active alignment and fixation for connecting the optical network unit and the planar microlens arrays block are still required. The space between the two adjacent optical beams coming out of the optical network unit is small since the optical network unit is formed by the thin-film deposition technology. This would make the interface of the optical network unit with the optoelectronic devices very complicated because the optoelectronic devices have not been shrunk accordingly to match the size of the optical network unit.